Junior Network Administrator flashcards
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32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- OSI Layer 3
- The Network layer, responsible for logical addressing (IP) and routing packets between networks. It selects the best path and does not guarantee delivery.
- TCP three-way handshake
- Connection setup using SYN, SYN-ACK, and ACK packets. It synchronizes sequence numbers and confirms both hosts are ready to exchange data reliably.
- Encapsulation
- The process of adding protocol headers as data moves down the OSI layers, producing a segment, packet, then frame before transmission on the medium.
- Private IPv4 ranges
- RFC 1918 addresses: 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16. They are not routed on the public Internet and require NAT for external access.
- Usable hosts formula
- For a subnet with h host bits, usable addresses = 2^h − 2. The two subtracted addresses are the network address and the directed broadcast address.
- Longest prefix match
- A router forwarding rule that chooses the route with the most specific (longest) subnet mask matching the destination. It overrides shorter, less specific routes.
- Default route
- The 0.0.0.0/0 (IPv4) or ::/0 (IPv6) route used when no more specific route matches the destination. It points toward the upstream gateway.
- CIDR /26 mask
- 255.255.255.192, providing 64 addresses per subnet and 62 usable hosts. Subnets increment by 64 in the last octet: .0, .64, .128, .192.
- Switch vs hub
- A switch forwards frames only to the destination MAC port, creating per-port collision domains. A hub repeats every frame to all ports, sharing one collision domain.
- Cat6a cable
- Shielded twisted-pair copper cabling rated for 10 Gbps Ethernet up to 100 meters. It reduces crosstalk compared with Cat6, which limits 10G to 55 m.
- Single-mode fiber
- Fiber with a small core (about 9 µm) carrying one light path, supporting very long distances and higher bandwidth. It typically uses laser sources and OS1/OS2 ratings.
- Star topology
- A layout where every device connects to a central switch or hub. It is easy to troubleshoot, but the central device is a single point of failure.
- 802.1Q trunking
- A standard that inserts a 4-byte tag into Ethernet frames to identify VLAN membership across trunk links. The native VLAN is sent untagged.
- VLAN access port
- A switch port assigned to one VLAN that sends and receives untagged frames. End devices such as PCs and printers connect to access ports.
- Spanning Tree Protocol
- A Layer 2 protocol that prevents switching loops by electing a root bridge and blocking redundant ports. RSTP (802.1w) provides faster convergence.
- MAC address table
- A switch database mapping learned source MAC addresses to ports. It enables frame filtering and forwarding instead of flooding to all ports.
- SSID
- The human-readable name that identifies a wireless network. Multiple access points can share one SSID to form an extended service set for roaming.
- WPA2-Personal
- A Wi-Fi security mode using a pre-shared key and AES-CCMP encryption. All users share the same passphrase, making key rotation and per-user accountability difficult.
- 2.4 GHz channels 1, 6, 11
- The three non-overlapping channels in the 2.4 GHz band in North America. Using them reduces co-channel and adjacent-channel interference between access points.
- CSMA/CA
- Carrier Sense Multiple Access with Collision Avoidance, the wireless medium access method. Stations listen, wait a random backoff, and optionally use RTS/CTS.
- DHCP DORA process
- The four-step lease process: Discover, Offer, Request, Acknowledgment. The client broadcasts Discover; the server replies with an Offer, then confirms the lease.
- DHCP relay
- A router feature (ip helper-address) that forwards DHCP broadcasts from a client subnet to a DHCP server on another subnet, enabling centralized address assignment.
- DNS A record
- A resource record that maps a hostname to an IPv4 address. AAAA records perform the equivalent mapping for IPv6 addresses.
- PAT (NAT overload)
- A NAT variant that translates many private inside addresses to one public address, using source port numbers to distinguish sessions.
- NTP stratum
- A hierarchy level indicating distance from a reference clock. Stratum 1 servers sync directly to stratum 0; each additional level increments the stratum number.
- CIA triad
- Confidentiality, Integrity, and Availability: the three core security goals. Encryption supports confidentiality, hashing supports integrity, and redundancy supports availability.
- Stateful firewall
- A firewall that tracks connection state and automatically permits return traffic for established sessions. It is more secure than stateless packet filtering.
- 802.1X
- Port-based network access control using a supplicant, an authenticator switch, and a RADIUS server. It blocks unauthorized devices until authentication succeeds.
- Port security
- A switch feature limiting the number of MAC addresses allowed on a port. Violations can protect, restrict, or shut down the port.
- Troubleshooting methodology
- A structured process: identify the problem, form a theory, test it, plan and implement a fix, verify functionality, and document the outcome.
- Traceroute
- A diagnostic tool that sends packets with increasing TTL values to reveal each router along the path. It reports per-hop latency and packet loss.
- CRC errors
- Frame check sequence failures counted on an interface. High counts usually indicate bad cabling, duplex mismatch, or interference rather than routing problems.